A printing press applies ink to an elongated web of paper as the web of paper is moved lengthwise through the printing press. The freshly printed paper web is moved through a drier, and is then moved through a chill roll assembly in order to cool the heated web and to set the ink. A chill roll assembly comprises a succession of rolls which are cooled by water circulating through the interior of the rolls.
As the paper web moves from the drier to the chill roll assembly, boundary layers of air adhere to the opposite side surfaces of the moving web and are carried along with the moving web. Vaporized chemical solvents and ink residue become trapped in the boundary layers on the side surfaces of the moving web as the web emerges from the drier, and are carried by the boundary layers toward the chill roll assembly.
As the moving web proceeds around the rolls in the chill roll assembly, the boundary layers have detrimental effects on the quality of the printed image on the web. The boundary layers adhering to the web surfaces are carried around the rolls in the chill roll assembly between the web surfaces and the roll surfaces. The boundary layers thereby insulate the heated surfaces of the web from the cooled surfaces of the rolls and inhibit heat transfer from the web to the rolls. Furthermore, the vaporized ink and chemical solvents in the boundary layers are deposited as residue on the roll surfaces as the web moves through the chill roll assembly. Ink residue accumulating on the roll surfaces can be transferred back onto the web to soil the printed web surfaces which follow.
U.S. Pat. No. 4,476,636 shows a means for clearing away the boundary layers on both sides of a printed paper web moving through a chill roll assembly. The chill roll assembly includes a pair of small boundary layer control rolls in sliding contact with the opposite side surfaces of the moving paper web. Each boundary layer control roll rotates in a direction opposite to the direction of the web sliding over the roll. A boundary layer carried on the web surface is squeezed off as the web surface slides against the boundary layer control roll.
Another known means for clearing away the boundary layer on the surface of a moving paper web in a chill roll assembly uses one of the chill rolls to affect the boundary layer instead of using a separate boundary layer control roll. In such a chill roll assembly, the paper web follows a horizontal path from the drier to the first one of the chill rolls, and continues in a serpentine path around the successive chill rolls. The chill rolls are mounted on a frame. The frame is pivotal about an axis in order to move the chill rolls relative to the horizontal web section extending from the oven to the first chill roll. The position of the frame can be adjusted to move the second chill roll into a position closely adjacent to the horizontal web section. The web section moving around the second chill roll is thus closely spaced from the horizontal web section. The closely spaced web sections move in opposite directions relative to one another. The closely spaced positions of the oppositely moving we sections define a zone of interference in which the boundary layers on the oppositely moving web sections are scrubbed or squeezed away. However, this arrangement of chill rolls affects only one side of the moving web.
An arrangement of chill rolls for scrubbing the boundary layers on both sides of the moving web is shown in U.S. Pat. No. 4,774,771. This patent shows four chill rolls mounted on a frame. The second and third chill rolls are adjustable on the frame. The axles of the second and third chill rolls are mounted at each end in an eccentric. Each of the eccentrics is adjustable on the frame to move the associated axle end horizontally and vertically on the frame. Adjustment of both ends of the second chill roll axle moves the second chill roll into a position closely spaced from the horizontal web section moving from the drier to the first chill roll. A first zone of interference is thereby defined for scrubbing the boundary layer on the upper side surface of the web. Adjustment of both ends of the third chill roll axle moves the third chill roll into a position closely spaced from the web section moving between the first chill roll and the second chill roll. A second zone of interference is thereby defined for scrubbing the boundary layer on the lower side surface of the web. However, the opposite ends of the movable chill roll axles must be carefully adjusted to maintain the chill rolls in parallel relationship and to define uniform zones of interference across the width of the web.